Polishing composition, method for producing polishing composition, polishing method, and method for producing semiconductor substrate

ABSTRACT

A polishing composition according to the present invention includes: silica; an anionic water-soluble polymer; at least one compound selected from the group consisting of a phosphonate group-containing compound, a phosphate group-containing compound, and an amino group-containing compound; and a dispersing medium.

CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND 1. Technical Field

The present invention relates to a polishing composition, a method forproducing a polishing composition, a polishing method, and a method forproducing a semiconductor substrate.

2. Description of Related Arts

In recent years, a so-called chemical mechanical polishing (CMP)technique for physically polishing and flattening a semiconductorsubstrate in producing a device is used in accordance with multilayerwiring on a surface of a semiconductor substrate. CMP is a method forflattening a surface of an object to be polished (material to bepolished) such as a semiconductor substrate by using a polishingcomposition (slurry) containing abrasive grains of silica, alumina,ceria, or the like, an anti-corrosion agent, a surfactant, and the like.Specifically, CMP is used in processes such as shallow trench isolation(STI), flattening of interlayer insulating films (ILD films), formationof tungsten plugs, and formation of multilayer wires composed of copperand a low dielectric film. In such CMP, it is required that aninsulating film (such as silicon nitride) and an electric conductivematerial (such as titanium nitride) are removed by polishing with a highpolishing selectivity (that is, the insulating film such as siliconnitride is removed at a higher polishing speed than that of the electricconductive material such as titanium nitride).

As a means for increasing polishing selectivity between silicon nitrideand titanium nitride, it is considered that a polishing speed oftitanium nitride is suppressed. For example, US 2015/221,521 A disclosesthat a polishing speed of titanium nitride is suppressed by using apolishing composition containing abrasive grains and a surfactant.

SUMMARY

However, the present inventor has found that when the object to bepolished containing silicon nitride and titanium nitride is polished byusing the polishing composition described in US 2015/221,521 A, a highpolishing speed ratio between silicon nitride and titanium nitride isnot still obtained particularly under a strong acidic condition (pH 2.5or less).

The present invention is made in view of the above-described problems,and an object thereof is to provide a polishing composition having asufficiently high polishing speed of silicon nitride with respect to apolishing speed of titanium nitride (that is, selectivity of siliconnitride/titanium nitride is high) even under a strong acidic condition(pH 2.5 or less).

The present inventor has conducted intensive studies in view of theabove-described problems. Consequently, the inventor found that theabove-described problems can be solved by using a polishing compositionincluding: silica;

an anionic water-soluble polymer; at least one compound selected fromthe group consisting of a phosphonate group-containing compound, aphosphate group-containing compound, and an amino group-containingcompound; and a dispersing medium, and achieved the present invention.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described. Incidentally, thepresent invention is not limited only to the following embodiments. Inaddition, in the present specification, unless specifically describedotherwise, operations and measurements of physical properties and thelike are performed under conditions of room temperature (20° C. orhigher and 25° C. or lower)/relative humidity of 40% RH or higher and50% RH or lower.

Incidentally, in the present specification, in specific compound names,notation “(meth)acrylic” means “acrylic” and “methacrylic” and notation“(meth)acrylate” means “acrylate” and “methacrylate.”

A polishing composition according to the present invention is expectedto be also effective to a general object to be polished containing aninsulating film and an electric conductive material. Examples of theinsulating film include silicon oxide and silicon nitride. Examples ofthe electric conductive material include titanium, titanium nitride,tantalum, and tantalum nitride. Of them, an object to be polishedcontaining silicon nitride (SiN) and titanium nitride (TiN) ispreferable since the polishing composition exhibits significant effectwith respect to the object to be polished. Specific examples of theobject to be polished containing silicon nitride (SiN) and titaniumnitride (TiN) include a semiconductor substrate having a structure inwhich a titanium nitride film is formed on a silicon nitride film and asemiconductor substrate having a structure in which all of a siliconnitride film and a titanium nitride film are exposed.

Herein, from the viewpoint of the effect exhibited by the presentinvention, it is preferable that the polishing composition according toan embodiment of the present invention is used in a step of polishing anobject to be polished containing silicon nitride and titanium nitride.The reason for this is speculated that in such an object to be polished,a polishing suppression action by the anionic water-soluble polymeralong with at least one compound selected from the group consisting of aphosphonate group-containing compound, a phosphate group-containingcompound, and an amino group-containing compound becomes stronger due toan action mechanism described below.

The present inventor speculates the mechanism that the above-describedproblems are solved by the present invention to be as follows. However,the following mechanism is merely speculation, and the scope of theinvention is not intended to be limited by the mechanism.

The polishing composition according to the present invention has afunction of suppressing the polishing speed of titanium nitride as aresult of interaction between each component contained in the polishingcomposition and the object to be polished. The polishing compositionaccording to the present invention contains silica, an anionicwater-soluble polymer, at least one compound selected from the groupconsisting of a phosphonate group-containing compound, a phosphategroup-containing compound, and an amino group-containing compound(hereinafter, simply also referred to as a TiN inhibitor), and adispersing medium. In a case where pH is acidic, since the surface ofthe titanium nitride film is positively charged, the anionicwater-soluble polymer is adsorbed to the titanium nitride film to form aprotective film on the surface of the titanium nitride film so thatpolishing of titanium nitride can be suppressed. However, as pH becomesmore acidic, adsorption of the anionic water-soluble polymer to titaniumnitride becomes weak, and thus the polishing speed of titanium nitridecannot be sufficiently suppressed. In this regard, the present inventorhas conducted intensive studies and found that the polishing speed oftitanium nitride can be suppressed by further adding the TiN inhibitor.The reason for this is as follows. The TiN inhibitor is polarized into apart having a positive electric charge and a part having a negativeelectric charge. The part having a negative electric charge can bestrongly adsorbed to the surface of the titanium nitride film even underthe strong acidic condition, but has a small molecular weight and doesnot sufficiently coat the surface of titanium nitride. However, when theTiN inhibitor and the anionic water-soluble polymer are concurrentlyused, the anionic water-soluble polymer is further electrically adsorbedto the part having a positive electric charge of the TiN inhibitor.Therefore, by concurrently using the TiN inhibitor and the anionicwater-soluble polymer, the surface of the titanium nitride film can besufficiently coated even under the strong acidic condition, theprotective film is formed, and thus the polishing speed can besuppressed. In particular, such an effect is significantly exhibitedunder a strong acidic condition with pH of 2.5 or less. From the abovedescription, it is considered that since the polishing composition ofthe present invention can suppress the polishing speed of titaniumnitride while polishing silicon nitride at a high speed, a highpolishing selectivity between silicon nitride and titanium nitride canbe realized. Thus, according to the present invention, there is provideda polishing composition having a sufficiently high polishing speed ofsilicon nitride with respect to a polishing speed of titanium nitride(that is, selectivity of silicon nitride/titanium nitride is high) evenunder a strong acidic condition (pH 2.5 or less).

(Silica)

The polishing composition according to the present invention containssilica. The silica contained in the polishing composition has an actionof mechanically polishing an object to be polished. The type of silicais not particularly limited, and examples thereof include colloidalsilica, fumed silica, and sol-gel method silica. Among these, from theviewpoint that solid-phase reaction between the polishing compositionand the object to be polished can be efficiently exerted, colloidalsilica is preferable.

Examples of a method for producing colloidal silica include a silicatesoda method and a sol-gel method, and colloidal silica produced by anyproduction method may be used. In addition, examples of commerciallyavailable products of colloidal silica include colloidal silicasmanufactured by Nissan Chemical Industries, Ltd., JGC Catalysts andChemicals Ltd., NIPPON CHEMICAL INDUSTRIAL CO., LTD., FUSO CHEMICAL CO.,LTD., ADEKA CORPORATION, Akzo Nobel Co., Ltd., AZ Electronic Materials,Nalco Chemical Company, and W. R. Grace & Co.—Conn.

The lower limit of the average primary particle size of silica ispreferably 6 nm or more, more preferably 8 nm or more, and furtherpreferably 10 nm or more. With such a range, since a high polishingspeed can be maintained, silica can be suitably used in a roughpolishing process or the like. In addition, the upper limit of theaverage primary particle size of silica is preferably 200 nm or less,more preferably 100 nm or less, further preferably 50 nm or less, andparticularly preferably 30 nm or less. With such a range, it is possibleto further suppress occurrence of defects on the surface of the objectto be polished after polishing. Incidentally, the average primaryparticle size of silica is calculated, for example, on the basis of aspecific surface area of silica measured by a BET method.

The lower limit of the average secondary particle size of silica ispreferably 15 nm or more, more preferably 20 nm or more, and furtherpreferably 25 nm or more. With such a range, since a high polishingspeed can be maintained, silica can be suitably used in the roughpolishing process. In addition, the upper limit of the average secondaryparticle size of silica is preferably 300 nm or less, more preferably200 nm or less, further preferably 100 nm or less, and particularlypreferably 50 nm or less. With such a range, it is possible to furthersuppress occurrence of defects on a surface of a silicon wafer afterpolishing. The average secondary particle size of silica can bemeasured, for example, by a dynamic light scattering method.

The content of silica is preferably 0.1% by mass or more, morepreferably 0.5% by mass or more, even more preferably 1.0% by mass ormore, and particularly preferably 1.4% by mass or more with respect tothe polishing composition. With such a range, a high polishing speed canbe maintained, and silica can be suitably used in the rough polishingprocess or the like. In addition, from the viewpoint of scratchprevention or the like, the content of silica is typically properly 10%by mass or less, preferably 5% by mass or less, more preferably 4% bymass or less, and particularly preferably 3% by mass or less. A smallercontent of silica is preferable also from the viewpoint of economicefficiency.

(Dispersing Medium)

The polishing composition according to the present invention contains adispersing medium for dispersing or dissolving each component. As thedispersing medium, it is preferable that water does not containimpurities as much as possible from the viewpoint of inhibitingcontamination of the object to be cleaned and action of othercomponents. As such water, for example, water in which the total contentof transition metal ions is 100 ppb or less is preferable. Herein, thepurity of water can be increased, for example, by an operation such asremoving impurity ions using an ion exchange resin, removing foreignsubstances using a filter, or distillation. Specifically, as water, forexample, deionized water (ion-exchanged water) , pure water, ultrapurewater, distilled water, and the like are preferably used.

The dispersing medium may be a mixed solvent of water and an organicsolvent in order to disperse or dissolve each component. In this case,examples of the organic solvent to be used include acetone,acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol,and propylene glycol that are organic solvents mixing with water. Inaddition, these organic solvents may be used without being mixed withwater, and may be mixed with water after each component is dispersed ordissolved. These organic solvents can be used either singly or incombination of two or more kinds thereof.

(Anionic Water-Soluble Polymer)

The polishing composition according to the present invention contains ananionic water-soluble polymer. The anionic water-soluble polymer in thepolishing composition is adsorbed to a surface of a titanium nitridelayer when the polishing composition is used for polishing the object tobe polished. According to this, the polishing composition according tothe present invention can suppress the polishing speed of titaniumnitride.

Examples of an anionic group of the anionic water-soluble polymerinclude a carboxylic group (carboxyl group), a sulfonic group, asulfuric acid ester group, a phosphoric acid ester group, and aphosphonate group, but from the viewpoint of reducing scratches andparticles, the anionic water-soluble polymer preferably has a carboxylicgroup and more preferably has only a carboxylic group. That is, in thepresent invention, the anionic water-soluble polymer is preferablypolycarboxylic acid. Incidentally, these anionic groups may be in theform of a neutralized salt.

Examples of a water-soluble polymer having a carboxylic group include a(co) polymer having a constituent unit derived from a monomer having acarboxylic group and a salt thereof. Examples of the monomer having acarboxylic group include itaconic acid, (meth) acrylic acid, maleicacid, and salts thereof. In the anionic water-soluble polymer, two ormore kinds of constituent unit derived from a monomer having acarboxylic group may be contained. Of them, as the anionic water-solublepolymer, poly (meth) acrylic acid, a (meth) acrylic acid-maleic acidcopolymer, or a salt thereof is exemplified.

The anionic water-soluble polymer may contain a constituent unitcomponent derived from a monomer other than the anionic group-containingmonomer within the range that the effect of the present invention isexhibited.

The content of the anionic water-soluble polymer in the polishingcomposition is preferably 1 ppm by mass or more, more preferably 10 ppmby mass or more, further preferably 100 ppm by mass or more, even morepreferably 1000 ppm by mass or more, and particularly preferably 2000ppm by mass or more. As the content of the anionic water-soluble polymerincreases, the anionic water-soluble polymer adsorbed on the titaniumnitride film increases so that the polishing speed of titanium nitridecan be effectively suppressed.

The content of the anionic water-soluble polymer in the polishingcomposition is also preferably 100000 ppm by mass or less, morepreferably 10000 ppm by mass or less, further preferably 8000 ppm bymass or less, even more preferably 6000 ppm by mass or less, andparticularly preferably 4000 ppm by mass or less. As the content of thewater-soluble polymer decreases, the abrasive grains in the polishingcomposition are less likely to aggregate. Thus, this provides anadvantageous effect of improving the storage stability of the polishingcomposition.

The weight average molecular weight (Mw) of the anionic water-solublepolymer in the polishing composition is preferably 1000 or more, morepreferably 1500 or more, further preferably 2000 or more, furtherpreferably 3000 or more, even more preferably 4000 or more, andparticularly preferably 4500 or more. As the molecular weight of theanionic water-soluble polymer increases, the sufficient amount of thepolymer to suppress the polishing speed of the titanium nitride layer bythe polishing composition is easily adsorbed on the surface of thetitanium nitride layer.

The weight average molecular weight (Mw) of the anionic water-solublepolymer in the polishing composition is preferably 10000 or less, morepreferably 6000 or less, further preferably 5500 or less, even morepreferably 5400 or less, and particularly preferably 5300 or less. Asthe molecular weight of the water-soluble polymer decreases, theabrasive grains in the polishing composition are less likely toaggregate. Thus, this provides an advantageous effect of improving thestorage stability of the polishing composition. As the weight averagemolecular weight of the polymer compound, a value of the weight averagemolecular weight (in terms of polyethyleneglycol) measured by gelpermeation chromatography (GPC) was used. The weight average molecularweight was measured by the following apparatus and conditions.

GPC apparatus: manufactured by SHIMADZU CORPORATION

Model: Prominence +ELSD detector (ELSD-LTII)

Column: VP-ODS (manufactured by SHIMADZU CORPORATION)

Mobile phase A: MeOH

-   -   B: aqueous solution of 1% acetic acid

Flow rate: 1 ml/min

Detector: ELSD temp. 40° C., Gain 8, N2 GAS 350 kPa

Oven temperature: 40° C.

Injection amount: 40 μL

(TiN Inhibitor)

The polishing composition according to the present invention contains atleast one compound selected from the group consisting of a phosphonategroup-containing compound, a phosphate group-containing compound, and anamino group-containing compound as a TiN inhibitor. In addition, asdescribed above, although the polishing speed of titanium nitride can besuppressed by addition of the anionic water-soluble polymer, thepolishing speed of titanium nitride can be further suppressed by addingthe TiN inhibitor.

As the pH of the polishing composition becomes more strongly acidic,even when only the anionic water-soluble polymer is used, thesuppression of the polishing speed of titanium nitride is notsufficient. In this regard, when the TiN inhibitor and the anionicwater-soluble polymer are concurrently used, the surface of the titaniumnitride film can be sufficiently coated even under the strong acidiccondition, and the polishing speed can be suppressed by forming aprotective film. Incidentally, either only one or a plurality of kindsof the TiN inhibitor may be used.

As the phosphonate group-containing compound which can be used as theTiN inhibitor, a compound having one to six phosphonate groups ispreferably exemplified. Specifically, examples of a compound having onephosphonate group include phosphonic acid, methyl phosphonic acid,phenyl phosphonic acid, and 1-naphthylmethyl phosphonic acid. Inaddition, examples of a compound having two phosphonate groups includemethylene diphosphonic acid (MDPNA), ethylene diphosphonic acid (EDPNA),1-hydroxyethane-1,1-diphosphonic acid (etidronic acid, HEDP),nitrilotris(methylenephosphonic acid) (NTMP), ethylenediaminetetraphosphonic acid, ethylenediamine tetramethylene phosphonic acid(EDTMP), and diethylenetriamine penta(methylenephosphonic acid) (DTPMP).Of the phosphonate group-containing compounds, compounds having two ormore, preferably three to five phosphonate groups in one molecule arepreferable. For example, it is particularly preferable that thephosphonate group-containing compound is nitrilotris(methylenephosphonicacid) (NTMP), ethylenediamine tetramethylene phosphonic acid (EDTMP),and diethylenetriamine penta(methylenephosphonic acid) (DTPMP).

Examples of the phosphate group-containing compound which can be used asthe TiN inhibitor include an inorganic phosphoric acid compound and anorganic phosphoric acid compound. Specific examples of the inorganicphosphoric acid compound include monophosphoric acids such as phosphoricacid (orthophosphoric acid), phosphorous acid, and hypophosphorous acid,polyphosphoric acids such as pyrophosphoric acid, pyrophosphorous acid,triphosphoric acid, tetraphosphoric acid, hexaphosphoric acid,cyclophosphoric acid, metaphosphoric acid, and hexametaphosphoric acid,and salts thereof. Specific examples of the organic phosphoric acidcompound include alkyl phosphoric acid esters such astetradecylphosphoric acid, hexadecylphosphoric acid, octadecylphosphoricacid, didecylphosphoric acid, 10-methacryloyloxy decyl dihydrogenphosphate, 12-acryloyloxy dodecyl dihydrogen phosphate,12-methacryloyloxy dodecyl dihydrogen phosphate, 16-acryloyloxyhexadecyl dihydrogen phosphate, 16-methacryloyloxy hexadecyl dihydrogenphosphate, 20-acryloyloxy icosyl dihydrogen phosphate,20-methacryloyloxy icosyl dihydrogen phosphate, bis[8-acryloyloxyoctyl]hydrogen phosphate, bis[8-methacryloyloxy octyl]hydrogenphosphate, bis[9-acryloyloxy nonyl]hydrogen phosphate,bis[9-methacryloyloxy nonyl]hydrogen phosphate, bis[10-acryloyloxydecyl]hydrogen phosphate, and bis[10-methacryloyloxy decyl]hydrogenphosphate; and pyrophosphoric acid esters such as pyrophosphoric acidbisoctyl, pyrophosphoric acid bis[8-acryloyloxy octyl], pyrophosphoricacid bis[8-methacryloyloxy octyl], pyrophosphoric acidbis[10-acryloyloxy decyl], and pyrophosphoric acidbis[10-methacryloyloxy decyl].

The content of the phosphonate group-containing compound or thephosphate group-containing compound in the polishing composition (in thecase of containing two or more kinds, the total content thereof) ispreferably 50 ppm by mass or more, more preferably 100 ppm by mass ormore, further preferably 120 ppm by mass or more, further preferably 150ppm by mass or more, further preferably 220 ppm by mass or more, furtherpreferably 240 ppm by mass or more, further preferably 260 ppm by massor more, and particularly preferably 270 ppm by mass or more. As thecontent of the phosphonate group-containing compound or the phosphategroup-containing compound increases, the content of the TiN inhibitor tobe adsorbed to the titanium nitride film increases, and thus thepolishing speed of titanium nitride can be effectively suppressed.

The content of the phosphonate group-containing compound or thephosphate group-containing compound in the polishing composition (in thecase of containing two or more kinds, the total content thereof) is alsopreferably 10000 ppm by mass or less, more preferably 1000 ppm by massor less, further preferably 800 ppm by mass or less, further preferably600 ppm by mass or less, further preferably 500 ppm by mass or less,further preferably 450 ppm by mass or less, and particularly preferably400 ppm by mass or less. As the content of the phosphonategroup-containing compound or the phosphate group-containing compounddecreases, the polishing speed of the object to be polished,particularly, silicon nitride contained in the object to be polished isless likely to decrease.

The molecular weight of the phosphonate group-containing compound or thephosphate group-containing compound in the polishing composition ispreferably less than 1000 and more preferably less than 600 from theviewpoint of the polishing speed of SiN. The phosphonategroup-containing compound or the phosphate group-containing compoundhaving a small molecular weight causes the polishing speed of SiN to beless likely to decrease.

Examples of the amino group-containing compound which can be used in thepolishing composition include an amino acid, amino group-containingpolyalkylene glycol, and aliphatic primary amine. Among these, an aminoacid is particularly preferable. The amino acid indicates an organiccompound having both functional groups of an amino group and a carboxylgroup. Specific examples of the amino acid include glycine, α-alanine,β-alanine, N-methylglycine, N,N-dimethylglycine, 2-aminobutyric acid,norvaline, valine, leucine, norleucine, isoleucine, phenylalanine,proline, sarcosine, ornithine, lysine, taurine, serine, threonine,homoserine, tyrosine, bicine, tricine, 3,5-diiodo-tyrosine,β-(3,4-dihydroxyphenyl)-alanine, thyroxine, 4-hydroxy-proline, cysteine,methionine, ethionine, lanthionine, cystathionine, cystine, cysteicacid, aspartic acid, glutamic acid, S-(carboxymethyl)-cysteine,4-aminobutyric acid, asparagine, glutamine, azaserine, arginine,canavanine, citrulline, δ-hydroxy-lysine, creatine, histidine,1-methyl-histidine, 3-methyl-histidine, and tryptophan. Of them, fromthe viewpoint of the polishing speed of SiN, a basic amino acid is morepreferable, and specifically, arginine, lysine, tryptophan, histidine,and citrulline are particularly preferable. Since the pH of thepolishing composition of the present invention is lower than anisoelectric point (iso-electrostatic point) of the basic amino acid,regardless of the basic amino acid being positively charged or being notcharged, the phosphonate group-containing compound or the phosphategroup-containing compound causes the polishing speed of SiN to be lesslikely to decrease.

The content of the amino group-containing compound in the polishingcomposition (in the case of containing two or more kinds, the totalcontent thereof) is preferably 100 ppm by mass or more, more preferably1000 ppm by mass or more, and further preferably 5000 ppm by mass ormore. With such a range, SiN can be polished at a high polishing speed.In addition, the content of the amino group-containing compound in thepolishing composition is preferably 100000 ppm by mass or less, morepreferably 50000 ppm by mass or less, further preferably 20000 ppm bymass or less, and particularly preferably 10000 ppm by mass or less.With such a range, the amount of a pH adjusting agent used for adjustingpH to a target pH can be decreased, and the effect of slurry stabilityis obtainable.

(pH and pH Adjusting Agent)

According to an embodiment of the present invention, the pH of thepolishing composition is also not particularly limited, but the lowerlimit thereof is preferably 1.0 or more, more preferably 1.5 or more,further preferably 1.7 or more, and particularly preferably 2.0 or more.Meanwhile, the upper limit thereof is preferably 7.0 or less, morepreferably 5.0 or less, further preferably 3.0 or less, and furtherpreferably 2.5 or less. Thus, according to an embodiment of the presentinvention, the pH of the polishing composition is 1.0 to 7.0. In view ofthe mechanism of the present invention, by employing such an embodiment,the effect of increasing selectivity during polishing is particularlysignificant.

As the pH adjusting agent, known acids, bases, and salts thereof can beused.

Specific examples of the acids which can be used as the pH adjustingagent include inorganic acids such as hydrochloric acid, sulfuric acid,nitric acid, hydrofluoric acid, boric acid, carbonic acid,hypophosphorous acid, phosphorous acid, and phosphoric acid, and organicacids such as formic acid, acetic acid, propionic acid, butyric acid,valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyricacid, 2-ethylbutyric acid, 4-methylpentanoic acid, n-heptanoic acid,2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoicacid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleicacid, phthalic acid, malic acid, gluconic acid, itaconic acid, tartaricacid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid,2,5-furandicarboxylic acid, 3-furancarboxylic acid,2-tetrahydrofurancarboxylic acid, methoxyacetic acid,methoxyphenylacetic acid, and phenoxyacetic acid. In a case where aninorganic acid is used as the pH adjusting agent, particularly, sulfuricacid, nitric acid, phosphoric acid, and the like are particularlypreferable from the viewpoint of improving the polishing speed, and in acase where an organic acid is used as the pH adjusting agent, glycolicacid, succinic acid, maleic acid, citric acid, tartaric acid, malicacid, gluconic acid, itaconic acid, and the like are preferable.

Specific examples of the bases which can be used as the pH adjustingagent include amines such as aliphatic amine and aromatic amine, organicbases such as quaternary ammonium hydroxide, hydroxides of alkali metalsuch as potassium hydroxide, hydroxides of alkaline-earth metal,tetramethylammonium hydroxide, and ammonia. Among these, from theviewpoint of ease of availability, potassium hydroxide or ammonia ispreferable.

The amount of the pH adjusting agent added is not particularly limited,and may be appropriately adjusted such that the polishing compositionhas a desired pH.

(Method for Producing Polishing Composition)

A method for producing the polishing composition according to thepresent invention is not particularly limited. For example, thepolishing composition can be obtained by mixing and stirring silica, ananionic water-soluble polymer, a TiN inhibitor, and as necessary, otheradditives in a dispersant. In an embodiment, there is provided a methodfor producing the polishing composition, the method including mixing thesilica, the anionic water-soluble polymer, the at least one compoundselected from the group consisting of a phosphonate group-containingcompound, a phosphate group-containing compound, and an aminogroup-containing compound, and the dispersing medium.

(Polishing Method)

In an embodiment, there is provided a polishing method including a stepof polishing an object to be polished by using the polishing compositionaccording to the present invention.

For example, a working slurry containing the polishing compositionaccording to the present invention is prepared. Next, the polishingcomposition is supplied to an object to be polished and the object to bepolished is polished by a general method. For example, the object to bepolished is set in a general polishing apparatus, and the polishingcomposition is supplied to the surface of the object to be polished(surface to be polished) through a polishing pad of the polishingapparatus. Typically, while the polishing composition is continuouslysupplied, the polishing pad is pressed against the surface of the objectto be polished and the polishing pad and the object to be polished arerelatively moved (for example, rotationally moved). The object to bepolished is subjected to this polishing step, whereby polishing of theobject to be polished ends.

The polishing pad used in the polishing step is not particularlylimited. For example, any polishing pad of a foamed polyurethane type, anon-woven fabric type, a suede type, including abrasive grains, and notincluding abrasive grains can be used. In addition, as the polishingapparatus, a double-side polishing apparatus which polishes bothsurfaces of the object to be polished may be used or a single-sidepolishing apparatus which polishes only one surface of the object to bepolished may be used.

The polishing composition may be used in an embodiment in which thepolishing composition once used is discarded (so-called “discarded aftersingle use”) or may be repeatedly used in recycle. One example of themethod of using the polishing composition in recycle includes collectingthe polishing composition after use, which is discharged from thepolishing apparatus into a tank, and supplying the collected polishingcomposition to the polishing apparatus again. In a case where thepolishing composition is used in recycle, the amount of the polishingcomposition after use, which is dealt with as wasted liquid, can bereduced as compared with the case of being discarded after single use,and thus environmental load can be reduced. Further, since the amount ofthe polishing composition used is reduced, the cost can be reduced.

Herein, in an embodiment, it is preferable that the object to bepolished contains silicon nitride and titanium nitride.

(Method for Producing Semiconductor Substrate)

In an embodiment, there is provided a method for producing asemiconductor substrate, the method including a step of polishing anobject to be polished by the polishing method.

Although the embodiments of the present invention have been described indetail, these are descriptive and illustrative rather than limited, andit is apparent that the scope of the present invention has to beunderstood with the appended claims.

The present invention includes the following aspects and embodiments.

-   1. A polishing composition containing:

silica;

an anionic water-soluble polymer;

at least one compound selected from the group consisting of aphosphonate group-containing compound, a phosphate group-containingcompound, and an amino group-containing compound; and

a dispersing medium.

-   2. The polishing composition described in the item 1, in which pH is    1.0 to 7.0.-   3. The polishing composition described in the item 1 or 2, in which    the anionic water-soluble polymer is polycarboxylic acid.-   4. The polishing composition described in any one of the items 1 to    3, in which the phosphonate group-containing compound has one to six    phosphonate groups.-   5. The polishing composition described in any one of the items 1 to    4, in which the phosphonate group-containing compound is at least    one selected from the group consisting of    nitrilotris(methylenephosphonic acid), ethylenediamine    tetramethylene phosphoric acid, and diethylenetriamine    penta(methylenephosphonic acid).-   6. The polishing composition described in any one of the items 1 to    5, in which the phosphate group-containing compound is at least one    selected from the group consisting of an inorganic phosphoric acid    compound and an organic phosphoric acid compound.-   7. The polishing composition described in any one of the items 1 to    6, in which the amino group-containing compound is an amino acid.-   8. The polishing composition described in any one of the items 1 to    7, in which the polishing composition is used in a step of polishing    an object to be polished containing silicon nitride and titanium    nitride.-   9. A method for producing the polishing composition described in    anyone of the items 1 to 8, the method including mixing the silica,    the anionic water-soluble polymer, the at least one compound    selected from the group consisting of a phosphonate group-containing    compound, a phosphate group-containing compound, and an amino    group-containing compound, and the dispersing medium.-   10. A polishing method including a step of polishing an object to be    polished by using the polishing composition described in any one of    the items 1 to 8.-   11. The polishing method described in the item 10, in which the    object to be polished contains silicon nitride and titanium nitride.-   12. A method for producing a semiconductor substrate, the method    including a step of polishing an object to be polished by the    polishing method described in the item 10 or 11.

EXAMPLES

The present invention will be described in more detail using thefollowing Examples and Comparative Examples. However, the technicalscope of the present invention is not intended to be limited only to thefollowing Examples. Incidentally, unless specifically describedotherwise, “ppm,” “%,” and “part(s)” mean “parts per million by mass,”“% by mass,” and “part(s) by mass,” respectively.

(Preparation of Polishing Composition)

Preparation of Polishing Composition of Example 1

2% by mass of colloidal silica (average primary particle size: 12 nm;average secondary particle size: 30 nm) with respect to the finalpolishing composition, 3200 ppm of polyacrylic acid (Mw=5000) withrespect to the final polishing composition, and 50 ppm ofdiethylenetriamine penta(methylenephosphonic acid) (DTPMP) with respectto the final polishing composition were added and an aqueous solution ofnitric acid (70%) and water (ultrapure water) were added such that a pHof the polishing composition would be 2.2, thereby preparing a polishingcomposition of Example 1. The pH value of the polishing composition ofExample 1 (liquid temperature: 25° C.) was confirmed by a pH meter(model: LAQUA (registered trademark) manufactured by HORIBA, Ltd.).

Preparation of Polishing Compositions of Examples 2 to 23 andComparative Examples 1 to 4

Polishing compositions of respective Examples and Comparative Exampleswere prepared in the similar manner to preparation of the polishingcomposition of Example 1, except that the type and/or content of eachcomponent were changed as presented in the following Table 1.Incidentally, “-” in the table indicates that the correspondingcomponent was not used.

(CMP Process)

The silicon nitride substrate and the titanium nitride substrate servingas the semiconductor substrates were polished using the polishingcomposition of each of Examples 1 to 23 and Comparative Examples 1 to 4under the following conditions. Herein, as the silicon nitride substrateand the titanium nitride substrate, a 300-mm wafer was used.

(Polishing Apparatus and Polishing Conditions)

Polishing apparatus: FREX (registered trademark) 300E manufactured byEBARA CORPORATION

Polishing pad: Dow IC1400

Polishing pressure: 2.0 psi (1 psi=6894.76 Pa, the same applieshereafter)

Rotation number of polishing table: 60 rpm

Rotation number of head: 61 rpm

Supply of polishing composition: discarded after single use

Supply amount of polishing composition: 300 ml/min

Polishing time: for 30 seconds

(Polishing Speed Evaluation)

The polishing speed of each object to be polished after polishingdescribed above was obtained using the following Equation 1. Theevaluation results are collectively presented in Table 1.

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack & \; \\{{{Polishing}\mspace{14mu}{{speed}\left( \text{nm/min} \right)}} = \frac{\begin{matrix}{\left\lbrack {{{Thickness}({nm})}\mspace{14mu}{of}\mspace{14mu}{substrate}\mspace{14mu}{before}\mspace{14mu}{polishing}} \right\rbrack -} \\\left\lbrack {{{Thickness}({nm})}\mspace{14mu}{of}\mspace{14mu}{substrate}\mspace{14mu}{after}\mspace{14mu}{polishing}} \right\rbrack\end{matrix}}{\left\lbrack {{Treatment}\mspace{14mu}{{time}\left( \min \right)}} \right\rbrack}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In addition, in Examples, evaluation was performed using each of thesilicon nitride substrate and the titanium nitride substrate, but evenin the case of using a substrate containing silicon nitride and titaniumnitride, or the like, it is speculated that the same result as describedabove is obtained.

TABLE 1 TiN inhibitor SiN TiN Anionic water-soluble polymer Number ofpolishing polishing Content phosphate Content speed speed SiN/TiN TypeMw (ppm) Type groups (ppm) (nm/min) (nm/min) selectivity Example 1Polyacrylic acid 5000 3200 DTPMP 5 50 503 438 1.15 Example 2 Polyacrylicacid 5000 3200 DTPMP 5 100 479 358 1.34 Example 3 Polyacrylic acid 50003200 DTPMP 5 150 457 13 35.15 Example 4 Polyacrylic acid 5000 3200 DTPMP5 180 444 11 40.36 Example 5 Polyacrylic acid 5000 3200 DTPMP 5 210 4349 48.22 Example 6 Polyacrylic acid 5000 3200 DTPMP 5 240 426 7 60.86Example 7 Polyacrylic acid 5000 3200 DTPMP 5 270 419 4 104.75 Example 8Polyacrylic acid 5000 3200 DTPMP 5 300 417 2.3 181.30 Example 9Polyacrylic acid 5000 3200 DTPMP 5 400 360 2.8 130.27 Example 10Polyacrylic acid 5000 3200 DTPMP 5 500 341 3.5 98.94 Example 11Polyacrylic acid 2000 3200 DTPMP 5 300 356 99 3.60 Example 12 Sodium3000 3200 DTPMP 5 300 377 174 2.17 polyacrylate Example 13 Ammonium 60003200 DTPMP 5 300 353 98 3.60 polyacrylate Example 14 Ammonium 10000 3200DTPMP 5 300 359 193 1.86 polyacrylate Example 15 (Acrylic 2800 3200DTPMP 5 300 325 18 18.06 acid-maleic acid) salt copolymer Example 16Polyacrylic acid 5000 3200 EDTMP 4 300 379 26 14.85 Example 17Polyacrylic acid 5000 3200 NTMP 3 1550 366 73 5.03 Example 18Polyacrylic acid 5000 3200 HEDP 2 1730 427 79 5.39 Example 19Polyacrylic acid 5000 3200 Phenyl 1 1860 541 283 1.91 phosphonic acidExample 20 Polyacrylic acid 5000 3200 Arginine — 9900 442 52 8.45Example 21 Polyacrylic acid 5000 1600 Arginine — 8000 476 72 6.61Example 22 Polyacrylic acid 5000 1600 Arginine — 4000 548 134 4.09Example 23 Polyacrylic acid 5000 1600 Arginine — 2000 519 214 2.42Comparative Polyacrylic acid 5000 3200 — — — 535 542 0.99 Example 1Comparative — — — DTPMP 5 300 309 480 0.64 Example 2 Comparative — — —Arginine — 8000 408 545 0.75 Example 3 Comparative — — — — — — 456 6650.69 Example 4

From the results of Table 1, it was found that in Examples 1 to 23 usingthe polishing composition of the present invention, the polishing speedof silicon nitride with respect to the polishing speed of titaniumnitride (SiN/TiN selectivity) is sufficiently high. On the other hand,in Comparative Examples 1 to 4 not having at least one of the anionicwater-soluble polymer and the TiN inhibitor, the SiN/TiN selectivity waslow. In addition, it was found that among Examples, the result ofExample 8 using DTPMP is extremely excellent.

The present application is based on Japanese Patent Application No.2017-185460 filed on Sep. 26, 2017, and a disclosed content thereof isincorporated herein as a whole by reference.

1.-12. (canceled)
 13. A polishing composition comprising: silica; ananionic water-soluble polymer; at least one compound selected from thegroup consisting of a phosphonate group-containing compound, a phosphategroup-containing compound, and an amino group-containing compound; and adispersing medium, wherein an anionic group of the anionic water-solublepolymer is selected from the group consisting of a carboxylic group(carboxyl group), a sulfonic group, a sulfuric acid ester group, aphosphoric acid ester group, and a phosphonate group, and a content ofthe anionic water-soluble polymer is 1600 ppm or more.
 14. The polishingcomposition according to claim 13, wherein the anionic water-solublepolymer comprises a (co)polymer having a constituent unit derived from amonomer having a carboxylic group and a salt thereof.
 15. The polishingcomposition according to claim 14, wherein the monomer having acarboxylic group is selected from the group consisting of itaconic acid,(meth)acrylic acid, maleic acid and a salt thereof.
 16. The polishingcomposition according to claim 13, wherein the anionic water-solublepolymer is selected from the group consisting of polyacrylic acid,polyacrylic acid salt, (acrylic acid-maleic acid) copolymer and (acrylicacid-maleic acid) salt copolymer.
 17. The polishing compositionaccording to claim 13, wherein a weight average molecular weight of theanionic water-soluble polymer is 1000 or more.
 18. The polishingcomposition according to claim 13, wherein the phosphonategroup-containing compound has one to six phosphonate groups.
 19. Thepolishing composition according to claim 13, wherein the phosphonategroup-containing compound is at least one selected from the groupconsisting of 1-hydroxyethane-1,1-diphosphonic acid,nitrilotris(methylenephosphonic acid), ethylenediamine tetramethylenephosphonic acid, and diethylenetriamine penta(methylenephosphonic acid).20. The polishing composition according to claim 13, wherein a pH of thepolishing composition is 2.5 or less.
 21. The polishing compositionaccording to claim 13, wherein the polishing composition is used in astep of polishing an object to be polished containing silicon nitrideand titanium nitride.
 22. A method for producing the polishingcomposition according to claim 13, the method comprising mixing thesilica, the anionic water-soluble polymer, the at least one compoundselected from the group consisting of a phosphonate group-containingcompound having one to six phosphonate groups, and the dispersingmedium, wherein an anionic group of the anionic water-soluble polymer isselected from the group consisting of a carboxylic group (carboxylgroup), a sulfonic group, a sulfuric acid ester group, a phosphoric acidester group, and a phosphonate group, and a content of the anionicwater-soluble polymer is 1600 ppm or more.
 23. A polishing methodcomprising a step of polishing an object to be polished by using thepolishing composition according to claim
 13. 24. The polishing methodaccording to claim 23, wherein the object to be polished containssilicon nitride and titanium nitride.
 25. A method for producing asemiconductor substrate, the method comprising a step of polishing anobject to be polished by the polishing method according to claim 23.